1. Field of the Invention
The present invention relates to a data processor including an access size control unit that converts an access size in an access request output from a master circuit to a slave circuit to a predetermined data size such that the slave circuit can accept the access request. The data processor according to the present invention is built on an LSI chip, or the like, and includes a processor such as a CPU, a digital signal processor (DSP) or an interface to a memory such as an SDRAM.
2. Description of the Related Art
For a recent data processor system that is built on a chip, the system includes a master circuit (bus master) and its slave circuits linked to the master circuit via an interfacing bus and data transfer is performed between the master circuit and the slave circuits, in compliance with pre-defined access requirements. Also, such system is required to incorporate other slave circuits that do not conform to initial design specifications. In some cases, a master circuit such as a CPU having 32-bit access size and a memory controller designed for data transfer to/from another master circuit such as a CPU having 64-bit access size are mounted on a same data processor system.
Heretofore, Access size incompatibility has been overcome by adding a command that makes the master circuit use a data size suitable for accessing the slave circuit or the access size of the slave circuit is modified.
Herein, a circuit that issues an access request to another circuit is referred to as a master circuit. In addition to circuits such as a CPU or DSP, image data processing circuits such as an MPEG decoder and a graphic accelerator also correspond to master circuits under this definition. Conversely, a circuit that receives an access request from another circuit and performs processing is referred to as a slave circuit. For example, a memory interface is a slave circuit.
To enhance the use efficiency of previously designed circuits, it is preferable to allow the circuits to be used without circuit modification. The reason is as follows. For short-term development of LSIs whose scale becomes larger and larger, it is preferable that LSI manufacturers use circuit modules that have been designed in-house and in their possession as their assets or purchased from an external source. By incorporating such modules into a new design LSI, the cost and work hours of design can be reduced. Such design assets are called Intellectual Properties (IPs). If the circuit modification needs to use the IPs when developing a system chip, the benefit of using the IPs is reduced. The inventors find a necessity for installing a master circuit and a slave circuit that have different access size with each other on a same data processor system without circuit modification of IPs.